Fluid Lines And Fittings

Question 1

What are the two types of fluid lines commonly found in aircraft?

Answer 1

Rigid metal lines

Flexible hoses

Question 2

What are aircraft plumbing lines usually made of?

Answer 2

Metal tubing
Flexible hose
Fittings

Question 3

Describe the method of classifying metal tube according to size.

Answer 3

Metal tubing is sized according to wall thickness and outside diameter.
Outside diameter is measured in 1/16th inch increments

Question 4

When installing stainless steel tubing, what type of fittings should be used?

Answer 4

Stainless steel fittings

Question 5

What is the function of the sleeve on a flare-tube fitting?

Answer 5

The nuts fit over the sleeve and draws the sleeve and tubing flare tightly against the male fitting to form the seal

Question 6

Describe the two types of flares commonly used on aircraft tubing

Answer 6

Single flare

Double flare

Question 7

How can you determine if a fitting is an AN type rather than an AC type?

Answer 7

AN fittings have a shoulder between the flare cone and the end of the threads
AC Fittings do not

Question 8

What are the most significant differences between AN and AC fittings?

Answer 8

AN fittings have sleeve length, thread pitch, shoulder between threads, and a flare cone

Question 9

How are standard AN and AC type fluid line fittings identified?

Answer 9

AN fluid lines
Colored either blue or black
Coarser threads, smaller shoulder between threads
37 degree cone

AC type fluid lines
Colored either gray or yellow
Completely threaded all the way to the 35 degree cone

Question 10

What are the names of the parts of a flareless tube fitting?

Answer 10

Nut
Ferrule
Sleeve

Question 11

How do you tell a flareless fitting from a flare type fitting?

Answer 11

Flareless fittings don’t have a flare cone and there is no space between the threads and the end of the fitting

Question 12

What is the effect of overtightening a flare-type fitting?

Answer 12

The sealing surface may be damaged or the flare cut off

Question 13

In addition to being securely clamped, what is an additional requirement for installing metal fuel, oil, and hydraulic lines?

Answer 13

The lines must be electrically bonded to the structure

Question 14

What is the advantage of a flexible Teflon hose over a regular hose?

Answer 14

Teflon hoses have a better resistance to chemicals

Higher strength properties at higher temps

Question 15

Describe the identification markings commonly found on flexible hoses

Answer 15

Lay line
Mil spec number (identification)
Manufacturers name or symbol 
Hose size
Date code

Question 16

What type of information is on a hose lay line?

Answer 16

Type of hose

Quarter/year of manufacture

Question 17

How can you determine if a flexible hose has been correctly/incorrectly installed?

Answer 17

Lay line will be straight if properly installed

Twisted lay line indicates incorrect installation

Question 18

What is the purpose of the identification stripe running along the length of a flexible hose?

Answer 18

Stripe is called a lay line and indicates if the hose has twisted during installation

Question 19

How are flexible hose sizes designated?

Answer 19

By inside diameter, measured in 1/16th inch increments

Question 20

What precautions must be observed when deburring the end of a tube after it is cut?

Answer 20

Wall thickness must not be reduced in size or fractured

Question 21

Describe the operation of quick disconnect couplings

Answer 21

Each half has a valve that is held open when coupled and is spring loaded closed when disconnected

Question 22

Why are quick disconnect fittings used?

Answer 22

To provide a quick means to connect or disconnect a fluid line without loss of fluid or entrance of air into the system

Question 23

How much slack must be left in a flexible hose during installation?

Answer 23

5-8% of the total hose length to allow for freedom of movement under pressure

Question 24

What happens to the tube when a flareless fitting has been overtightened?

Answer 24

Tube is weakened when the nut drives the cutting edge of the sleeve too deeply into tube

Question 25

What material should be selected for high pressure rigid fluid lines?

Answer 25

Annealed

1/4 hard corrosion resistant steel

Question 26

What percentage of flattening is allowed when bending metal tubing?

Answer 26

25% max

Must maintain 75% of the original tube diameter